The convective grey zone

Representing deep convection is a challenging aspect in numerical atmospheric simulation at 1 to 10-kilometre resolution. In this range of grid-lengths often referred to as the “grey-zone”, numerical models must recognise the realism of both explicit (resolved) and implicit (sub-grid) deep convection. Employing a conventional convective parametrization scheme (CPS), which purposely suppresses explicit convection via assumptions suitable for coarser resolutions, is not ideal for grey-zone convective modelling. Nevertheless, the lack of any representation of sub-grid convection will lead to unrealistic accumulation of instability and subsequently delayed and explosive onset of convection. This project attempts to develop a new CPS for the grey-zone with a prognostic plume height and a stochastic triggering function based on the occurrence and strength of boundary layer thermals.

Some links for this work:

Thesis:

1. A PhD thesis describing the scheme and its testing for diurnal cycle simulations.

Poster:

1. A poster showing some preliminary results from the scheme, (presented by Jonathan Chui), at the MOAP annual meeting at the Met Office.